eina: allow eina_time_get to fall back to other clocks if the first one fails

eina: allow eina_time_get to fall back to other clocks if the first one fails

Summary:
eina_time_get tries to use only one clock which is defined at compile-time and
returns the result of that one. This causes problems on platforms where eg.
CLOCK_PROCESS_CPUTIME_ID is defined but the clock is actually not implemented
(ie. clock_gettime returns EINVAL), as we simply don't get any time at all.

Instead, make sure we include the code for all defined clocks and simply fall
back to other clocks if the previous ones aren't implemented.

Reviewers: cedric, raster

Reviewed By: cedric

CC: cedric
Differential Revision: https://phab.enlightenment.org/D547

Signed-off-by: Cedric BAIL <cedric.bail@samsung.com>